There have heretofore been widely used DC/DC converter devices as switching power supplies, having switching devices therein such as MOSFETs, IGBTs, or the like.
For example, there has been proposed a vehicle (hereinafter referred to as an “electric vehicle”) having a motor as a propulsive source, and incorporating a DC/DC converter apparatus therein for increasing and reducing a DC voltage, which is connected between an electricity storage device and a motor which is energized by an inverter. On the electric vehicle, when the motor is energized, the voltage across the electricity storage device is increased by the DC/DC converter apparatus and applied to the inverter. When the motor regenerates electric power, the regenerated voltage from the inverter is lowered by the DC/DC converter apparatus and is applied in order to charge the electricity storage device.
There has also been proposed another electric vehicle (hereinafter referred to as a “fuel cell vehicle”), which also uses a motor as a propulsive source. The fuel cell vehicle includes a fuel cell connected directly to the motor which is energized by an inverter. A DC/DC converter apparatus for increasing and reducing a DC voltage is connected between an electricity storage device and a junction between the fuel cell and the motor. The fuel cell is used as a main power supply, and the electricity storage device is used as an auxiliary power supply for assisting the main power supply.
On the fuel cell vehicle, when the motor is energized, the voltage across the fuel cell and the voltage across the electricity storage device, which has been increased by the DC/DC converter apparatus, are added together, and the sum of these voltages is applied to the inverter. When the motor regenerates electric power, the regenerated voltage from the inverter is lowered by the DC/DC converter apparatus and is applied in order to charge the electricity storage device. If the electric power generated by the fuel cell contains an excessive amount of electric power, the electric power is lowered in voltage and then is applied in order to charge the electricity storage device.
The DC/DC converter apparatus comprises a semiconductor module (switching module) including switching devices and diodes. Among these components, the switching devices in particular need to be sufficiently cooled, as the switching devices emit substantial heat when energized. Generally, a cooling apparatus with cooling fluid passages is used for water-cooling the switching module. In view of its usage on vehicles or the like, it is important for the cooling apparatus to have a sufficient cooling capability as well as a small size.
For example, Japanese Laid-Open Patent Publication No. 2002-093974 discloses a cooling apparatus for cooling power semiconductor devices of a power module on a series hybrid vehicle. In order to increase the cooling capability of the cooling apparatus, and to reduce the overall size of the power module, freewheeling diodes of an inverter connected to a generator and switching devices of an inverter of a motor are arrayed in respective phases along straight lines on a cooling plate, and cooling fluid pipes are disposed along the straight lines in the respective phases. In other words, the cooling fluid pipes are disposed along the components that produce intensive heat when the switching devices are energized. The components which are not used when electric power is generated by the generator are not cooled. Further, the number of bends of the cooling fluid passages is reduced, so that the cooling system can be reduced in size.